Aerosol containers have been commonly used to dispense personal, household, industrial, and medical products, and to provide a low cost, easy to use method of dispensing a product. Typically, aerosol containers include a product to be dispensed and a propellant used to discharge the product from the container. The propellant is under pressure and provides a force to expel the product when a user actuates the aerosol container.
More specifically, the product to be dispensed can include volatile actives such as fragrances, sanitizers, cleaners, waxes or other surface treatments, deodorizers and or insect control agents such as repellents, insecticides, or growth regulators. One or more chemicals to be dispensed are usually mixed in a solvent and, in any event, are mixed with the propellant. Typical propellants are compressed air or other compressed gases, carbon dioxide, a selected hydrocarbon gas, or mixtures of hydrocarbon gases, such as a propane-butane mix. The mixture is then sprayed out of the container by manually pushing down or sideways on an actuator button, lever, or other structure that controls a valve assembly mounted at the top of the container.
The two main types of propellants used in aerosol containers today are liquefied gas propellants, such as hydrocarbon and hydrofluorocarbon (HFC) propellants, and compressed gas propellants, such as compressed carbon dioxide or nitrogen gas. To a lesser extent, chlorofluorocarbon propellants (CFCs) are also used. The use of CFCs is, however, being phased out due to the harmful effects of CFCs on the environment. Hydrocarbon propellants contain Volatile Organic Compounds (VOCs). The content of VOCs in aerosol air fresheners is an unwanted byproduct and is consequently regulated by various federal and state regulatory agencies, such as the Environmental Protection Agency (EPA) and California Air Resource Board (CARB).
One way in which to reduce the VOC content released by aerosol containers is to reduce the content of the hydrocarbon propellant used to dispense the liquid product. However, a reduction in the propellant content adversely affects the product performance. Specifically, reducing the propellant content results in excessive amounts of the product remaining in the container at the end of the life of the dispenser assembly, and an increase in the size of particles of the dispensed product.
In other solutions, a piston is slidably sealed within the container and in between the product and the propellant so as to seal in the propellant. As the product is dispensed, the piston maintains pressure on the product and prevents release of the propellant by translating longitudinally within the container in contact with the inner wall of the container. For proper operation, the piston must form and maintain an effective seal with the inner wall of the container. If the piston fails to seal, the product to be dispensed may leak into the propellant. This leakage reduces the amount of product which can be dispensed. Moreover, for certain types of products and propellants, the leaked product may spoil. Additionally, when the piston seal fails, the propellant may leak into the product, which is known as blow by, and may also create problems.
Furthermore, discontinuities in the inner wall of a container make it difficult to maintain an effective seal between the piston and the side wall. Discontinuities can be either consistent, for example a seam, or random, for example a dent. Such discontinuities can cause the seal to fail or the piston to bind, or both. The likelihood of either seal failure or piston binding is dependent on both the longitudinal and radial rigidity of the piston. That is, a piston having a high radial rigidity is likely to leak or bind when it encounters a discontinuity. A piston having a high longitudinal rigidity is likely to bind when it encounters a discontinuity.
Existing piston designs incorporate a flexible skirt to provide an effective seal for an aerosol container. Accordingly, a common piston configuration is a one-piece molded plastic piston having a face portion and a flexible skirt for sealingly engaging the inner wall of the aerosol container. The plastic piston may also be manufactured by thermoforming, casting, pressing, extrusion, or any other process for manufacturing plastics. The longitudinal and radial rigidity of the piston are generally determined by the length and the thickness of the plastic skirt. One-piece molding or any other process of forming the piston, however, inherently limits how thin the skirt can be made. If the skirt is made too thin, molten plastic will not consistently and evenly fill the mold. If the skirt is made too thick, the piston will leak or bind.
Therefore, multiple needs exist for an improved aerosol container that minimizes the release of pollutants while performing efficiently and consistently throughout the life of the aerosol container. More specifically, needs exist for a barrier piston that isolates the product from the propellant, provides stability within the container, and conforms to variations in the container while using the pressurized propellant to discharge the product. Furthermore, needs exist for a more efficient method of molding such a barrier piston with an integrated seal.